1
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Bell TA, Luce BE, Hakim P, Ananda VY, Dardari H, Nguyen TH, Monshizadeh A, Chao LH. Prominin 1 and Tweety Homology 1 both induce extracellular vesicle formation. bioRxiv 2024:2023.11.08.566258. [PMID: 37986829 PMCID: PMC10659291 DOI: 10.1101/2023.11.08.566258] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2023]
Abstract
Prominin-1 (Prom1) is a five-transmembrane-pass integral membrane protein that associates with curved regions of the plasma membrane. Prom1 interacts with membrane cholesterol and actively remodels the plasma membrane. Membrane bending activity is particularly evident in photoreceptors, where Prom1 loss-of-function mutations cause failure of outer segment homeostasis, leading to cone-rod retinal dystrophy (CRRD). The Tweety Homology (Ttyh) protein family has been proposed to be homologous to Prominin, but it is not known whether Ttyh proteins have an analogous membrane-bending function. Here, we characterize the membrane-bending activity of human Prom1 and Ttyh1 in native bilayer membranes. We find that Prom1 and Ttyh1 both induce formation of extracellular vesicles (EVs) in cultured mammalian cells and that the EVs produced are biophysically similar. Ttyh1 is more abundant in EV membranes than Prom1 and produces EVs with membranes that are more tubulated than Prom1 EVs. We further show that Prom1 interacts more stably with membrane cholesterol than Ttyh1 and that this may contribute to membrane bending inhibition in Prom1 EVs. Intriguingly, a loss-of-function mutation in Prom1 associated with CRRD induces particularly stable cholesterol binding. These experiments provide mechanistic insight into Prominin function in CRRD and suggest that Prom and Ttyh belong to a single family of functionally related membrane-bending, EV-generating proteins.
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Affiliation(s)
- Tristan A Bell
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA, 02114
- Department of Genetics, Blavatnik Institute, Harvard Medical School, Boston, MA, 02115
| | - Bridget E Luce
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA, 02114
| | - Pusparanee Hakim
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA, 02114
| | - Virly Y Ananda
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA, 02114
| | - Hiba Dardari
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA, 02114
| | - Tran H Nguyen
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA, 02114
| | - Arezu Monshizadeh
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA, 02114
| | - Luke H Chao
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA, 02114
- Department of Genetics, Blavatnik Institute, Harvard Medical School, Boston, MA, 02115
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2
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Fry MY, Navarro PP, Hakim P, Ananda VY, Qin X, Landoni JC, Rath S, Inde Z, Lugo CM, Luce BE, Ge Y, McDonald JL, Ali I, Ha LL, Kleinstiver BP, Chan DC, Sarosiek KA, Chao LH. In situ architecture of Opa1-dependent mitochondrial cristae remodeling. EMBO J 2024; 43:391-413. [PMID: 38225406 PMCID: PMC10897290 DOI: 10.1038/s44318-024-00027-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2023] [Revised: 12/15/2023] [Accepted: 12/22/2023] [Indexed: 01/17/2024] Open
Abstract
Cristae membrane state plays a central role in regulating mitochondrial function and cellular metabolism. The protein Optic atrophy 1 (Opa1) is an important crista remodeler that exists as two forms in the mitochondrion, a membrane-anchored long form (l-Opa1) and a processed short form (s-Opa1). The mechanisms for how Opa1 influences cristae shape have remained unclear due to lack of native three-dimensional views of cristae. We perform in situ cryo-electron tomography of cryo-focused ion beam milled mouse embryonic fibroblasts with defined Opa1 states to understand how each form of Opa1 influences cristae architecture. In our tomograms, we observe a variety of cristae shapes with distinct trends dependent on s-Opa1:l-Opa1 balance. Increased l-Opa1 levels promote cristae stacking and elongated mitochondria, while increased s-Opa1 levels correlated with irregular cristae packing and round mitochondria shape. Functional assays indicate a role for l-Opa1 in wild-type apoptotic and calcium handling responses, and show a compromised respiratory function under Opa1 imbalance. In summary, we provide three-dimensional visualization of cristae architecture to reveal relationships between mitochondrial ultrastructure and cellular function dependent on Opa1-mediated membrane remodeling.
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Affiliation(s)
- Michelle Y Fry
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA, USA
- Department of Genetics, Blavatnik Institute, Harvard Medical School, Boston, MA, USA
| | - Paula P Navarro
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA, USA
- Department of Genetics, Blavatnik Institute, Harvard Medical School, Boston, MA, USA
- Department of Microbiology, Blavatnik Institute, Harvard Medical School, Boston, MA, USA
| | - Pusparanee Hakim
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA, USA
| | - Virly Y Ananda
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA, USA
| | - Xingping Qin
- John B. Little Center for Radiation Sciences, Harvard T.H. Chan School of Public Health, Boston, MA, USA
- Molecular and Integrative Physiological Sciences (MIPS) Program, Harvard T.H. Chan School of Public Health, Boston, MA, USA
- Lab of Systems Pharmacology, Harvard Program in Therapeutic Science, Department of Systems Biology, Harvard Medical School, Boston, MA, USA
| | - Juan C Landoni
- Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Sneha Rath
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA, USA
| | - Zintis Inde
- John B. Little Center for Radiation Sciences, Harvard T.H. Chan School of Public Health, Boston, MA, USA
- Molecular and Integrative Physiological Sciences (MIPS) Program, Harvard T.H. Chan School of Public Health, Boston, MA, USA
- Lab of Systems Pharmacology, Harvard Program in Therapeutic Science, Department of Systems Biology, Harvard Medical School, Boston, MA, USA
| | | | - Bridget E Luce
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA, USA
| | - Yifan Ge
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA, USA
- Department of Genetics, Blavatnik Institute, Harvard Medical School, Boston, MA, USA
- Interdisciplinary Research Center of Biology and Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Science, Shanghai, China
| | - Julie L McDonald
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA, USA
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Ilzat Ali
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA, USA
- Department of Genetics, Blavatnik Institute, Harvard Medical School, Boston, MA, USA
| | - Leillani L Ha
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, USA
- Department of Pathology, Massachusetts General Hospital, Boston, MA, USA
| | - Benjamin P Kleinstiver
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, USA
- Department of Pathology, Massachusetts General Hospital, Boston, MA, USA
- Department of Pathology, Harvard Medical School, Boston, MA, USA
| | - David C Chan
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Kristopher A Sarosiek
- John B. Little Center for Radiation Sciences, Harvard T.H. Chan School of Public Health, Boston, MA, USA
- Molecular and Integrative Physiological Sciences (MIPS) Program, Harvard T.H. Chan School of Public Health, Boston, MA, USA
- Lab of Systems Pharmacology, Harvard Program in Therapeutic Science, Department of Systems Biology, Harvard Medical School, Boston, MA, USA
| | - Luke H Chao
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA, USA.
- Department of Genetics, Blavatnik Institute, Harvard Medical School, Boston, MA, USA.
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3
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Boopathy S, Makhlouta Lugo C, Luce BE, McDonald J, Hakim P, Ponce J, Ueberheide BM, Chao LH. Identification of SLC25A46 interaction interfaces with mitochondrial membrane fusogens Mfn2 and Opa1. bioRxiv 2023:2023.12.29.573615. [PMID: 38234813 PMCID: PMC10793391 DOI: 10.1101/2023.12.29.573615] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2024]
Abstract
Mitochondrial fusion requires the sequential merger of four bilayers to two. The outer-membrane solute carrier protein SLC25A46 interacts with both the outer and inner-membrane dynamin family GTPases Mfn1/2 and Opa1. While SLC25A46 levels are known affect mitochondrial morphology, how SLC25A46 interacts with Mfn1/2 and Opa1 to regulate membrane fusion is not understood. In this study, we use crosslinking mass-spectrometry and AlphaFold 2 modeling to identify interfaces mediating a SLC25A46-Opa1-Mfn1/2 complex. We reveal that the bundle signaling element of Opa1 interacts with SLC25A46, and the helical repeat 1 region of Mfn2 interacts with the SLC25A46 N-terminus. We validate these newly identified interaction interfaces and show that they play a role in mitochondrial network maintenance.
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Affiliation(s)
- Sivakumar Boopathy
- Department of Molecular Biology, Massachusetts General Hospital, Boston MA 02114, USA
- Department of Genetics, Harvard Medical School, Boston MA 02115, USA
| | - Camila Makhlouta Lugo
- Department of Molecular Biology, Massachusetts General Hospital, Boston MA 02114, USA
| | - Bridget E Luce
- Department of Molecular Biology, Massachusetts General Hospital, Boston MA 02114, USA
| | - Julie McDonald
- Department of Molecular Biology, Massachusetts General Hospital, Boston MA 02114, USA
| | - Pusparanee Hakim
- Department of Molecular Biology, Massachusetts General Hospital, Boston MA 02114, USA
| | - Jackeline Ponce
- Proteomics Resource Center, Division of Advanced Research Technologies, New York University Langone Health Center, New York NY 10016, USA
| | - Beatrix M Ueberheide
- Proteomics Resource Center, Division of Advanced Research Technologies, New York University Langone Health Center, New York NY 10016, USA
- Department of Biochemistry and Molecular Pharmacology, New York University Langone Health Center, New York NY 10016, USA
| | - Luke H Chao
- Department of Molecular Biology, Massachusetts General Hospital, Boston MA 02114, USA
- Department of Genetics, Harvard Medical School, Boston MA 02115, USA
- Corresponding author
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4
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Fry MY, Navarro PP, Hakim P, Ananda VY, Qin X, Landoni JC, Rath S, Inde Z, Lugo CM, Luce BE, Ge Y, McDonald JL, Ali I, Ha LL, Kleinstiver BP, Chan DC, Sarosiek KA, Chao LH. In situ architecture of Opa1-dependent mitochondrial cristae remodeling. bioRxiv 2023:2023.01.16.524176. [PMID: 36711707 PMCID: PMC9882235 DOI: 10.1101/2023.01.16.524176] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Cristae membrane state plays a central role in regulating mitochondrial function and cellular metabolism. The protein Optic atrophy 1 (Opa1) is an important crista remodeler that exists as two forms in the mitochondrion, a membrane-anchored long form (l-Opa1) and a processed short form (s-Opa1). The mechanisms for how Opa1 influences cristae shape have remained unclear due to lack of native three-dimensional views of cristae. We perform in situ cryo-electron tomography of cryo-focused ion beam milled mouse embryonic fibroblasts with defined Opa1 states to understand how each form of Opa1 influences cristae architecture. In our tomograms, we observe a variety of cristae shapes with distinct trends dependent on s-Opa1:l-Opa1 balance. Increased l-Opa1 levels promote cristae stacking and elongated mitochondria while increased s-Opa1 levels correlated with irregular cristae packing and round mitochondria shape. Functional assays indicate a role for l-Opa1 in wild-type apoptotic and calcium handling responses, and compromised respiratory function under Opa1 imbalance. In summary, we provide three-dimensional visualization of cristae architecture to reveal relationships between mitochondrial ultrastructure and cellular function dependent on Opa1-mediated membrane remodeling.
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Affiliation(s)
- Michelle Y. Fry
- Department of Molecular Biology, Massachusetts General Hospital, Boston, USA
- Department of Genetics, Blavatnik Institute, Harvard Medical School, Boston, USA
| | - Paula P. Navarro
- Department of Molecular Biology, Massachusetts General Hospital, Boston, USA
- Department of Genetics, Blavatnik Institute, Harvard Medical School, Boston, USA
| | - Pusparanee Hakim
- Department of Molecular Biology, Massachusetts General Hospital, Boston, USA
| | - Virly Y. Ananda
- Department of Molecular Biology, Massachusetts General Hospital, Boston, USA
| | - Xingping Qin
- John B. Little Center for Radiation Sciences, Harvard T.H. Chan School of Public Health, Boston, USA
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, USA
- Molecular and Integrative Physiological Sciences (MIPS) Program, Harvard T.H. Chan School of Public Health, Boston, USA
| | - Juan C. Landoni
- Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Sneha Rath
- Department of Molecular Biology, Massachusetts General Hospital, Boston, USA
| | - Zintis Inde
- John B. Little Center for Radiation Sciences, Harvard T.H. Chan School of Public Health, Boston, USA
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, USA
- Molecular and Integrative Physiological Sciences (MIPS) Program, Harvard T.H. Chan School of Public Health, Boston, USA
| | | | - Bridget E. Luce
- Department of Molecular Biology, Massachusetts General Hospital, Boston, USA
| | - Yifan Ge
- Department of Molecular Biology, Massachusetts General Hospital, Boston, USA
- Department of Genetics, Blavatnik Institute, Harvard Medical School, Boston, USA
- Current address: Interdisciplinary Research Center of Biology and Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Science, China
| | - Julie L. McDonald
- Department of Molecular Biology, Massachusetts General Hospital, Boston, USA
- Current address: Massachusetts Institute of Technology, Biology, Cambridge, USA
| | - Ilzat Ali
- Department of Molecular Biology, Massachusetts General Hospital, Boston, USA
- Department of Genetics, Blavatnik Institute, Harvard Medical School, Boston, USA
| | - Leillani L. Ha
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, USA
- Department of Pathology, Massachusetts General Hospital, Boston, USA
| | - Benjamin P. Kleinstiver
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, USA
- Department of Pathology, Massachusetts General Hospital, Boston, USA
- Department of Pathology, Harvard Medical School, Boston, USA
| | - David C. Chan
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, USA
| | - Kristopher A. Sarosiek
- John B. Little Center for Radiation Sciences, Harvard T.H. Chan School of Public Health, Boston, USA
- Molecular and Integrative Physiological Sciences (MIPS) Program, Harvard T.H. Chan School of Public Health, Boston, USA
- Lab of Systems Pharmacology, Harvard Program in Therapeutic Science, Department of Systems Biology, Harvard Medical School, Boston, MA, USA
| | - Luke H. Chao
- Department of Molecular Biology, Massachusetts General Hospital, Boston, USA
- Department of Genetics, Blavatnik Institute, Harvard Medical School, Boston, USA
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5
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Hakim P, Hoang Y, Vecchiarelli AG. Dissection of the ATPase active site of McdA reveals the sequential steps essential for carboxysome distribution. Mol Biol Cell 2021; 32:ar11. [PMID: 34406783 PMCID: PMC8684754 DOI: 10.1091/mbc.e21-03-0151] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Carboxysomes, the most prevalent and well-studied anabolic bacterial microcompartment, play a central role in efficient carbon fixation by cyanobacteria and proteobacteria. In previous studies, we identified the two-component system called McdAB that spatially distributes carboxysomes across the bacterial nucleoid. Maintenance of carboxysome distribution protein A (McdA), a partition protein A (ParA)-like ATPase, forms a dynamic oscillating gradient on the nucleoid in response to the carboxysome-localized Maintenance of carboxysome distribution protein B (McdB). As McdB stimulates McdA ATPase activity, McdA is removed from the nucleoid in the vicinity of carboxysomes, propelling these proteinaceous cargos toward regions of highest McdA concentration via a Brownian-ratchet mechanism. How the ATPase cycle of McdA governs its in vivo dynamics and carboxysome positioning remains unresolved. Here, by strategically introducing amino acid substitutions in the ATP-binding region of McdA, we sequentially trap McdA at specific steps in its ATP cycle. We map out critical events in the ATPase cycle of McdA that allows the protein to bind ATP, dimerize, change its conformation into a DNA-binding state, interact with McdB-bound carboxysomes, hydrolyze ATP, and release from the nucleoid. We also find that McdA is a member of a previously unstudied subset of ParA family ATPases, harboring unique interactions with ATP and the nucleoid for trafficking their cognate intracellular cargos.
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Affiliation(s)
- Pusparanee Hakim
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109
| | - Y Hoang
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109
| | - Anthony G Vecchiarelli
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109
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6
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MacCready JS, Tran L, Basalla JL, Hakim P, Vecchiarelli AG. The McdAB system positions α-carboxysomes in proteobacteria. Mol Microbiol 2021; 116:277-297. [PMID: 33638215 PMCID: PMC8359340 DOI: 10.1111/mmi.14708] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Revised: 02/23/2021] [Accepted: 02/24/2021] [Indexed: 02/06/2023]
Abstract
Carboxysomes are protein-based organelles essential for carbon fixation in cyanobacteria and proteobacteria. Previously, we showed that the cyanobacterial nucleoid is used to equally space out β-carboxysomes across cell lengths by a two-component system (McdAB) in the model cyanobacterium Synechococcus elongatus PCC 7942. More recently, we found that McdAB systems are widespread among β-cyanobacteria, which possess β-carboxysomes, but are absent in α-cyanobacteria, which possess structurally and phyletically distinct α-carboxysomes. Cyanobacterial α-carboxysomes are thought to have arisen in proteobacteria and then horizontally transferred into cyanobacteria, which suggests that α-carboxysomes in proteobacteria may also lack the McdAB system. Here, using the model chemoautotrophic proteobacterium Halothiobacillus neapolitanus, we show that a McdAB system distinct from that of β-cyanobacteria operates to position α-carboxysomes across cell lengths. We further show that this system is widespread among α-carboxysome-containing proteobacteria and that cyanobacteria likely inherited an α-carboxysome operon from a proteobacterium lacking the mcdAB locus. These results demonstrate that McdAB is a cross-phylum two-component system necessary for positioning both α- and β-carboxysomes. The findings have further implications for understanding the positioning of other protein-based bacterial organelles involved in diverse metabolic processes. PLAIN LANGUAGE SUMMARY: Cyanobacteria are well known to fix atmospheric CO2 into sugars using the enzyme Rubisco. Less appreciated are the carbon-fixing abilities of proteobacteria with diverse metabolisms. Bacterial Rubisco is housed within organelles called carboxysomes that increase enzymatic efficiency. Here we show that proteobacterial carboxysomes are distributed in the cell by two proteins, McdA and McdB. McdA on the nucleoid interacts with McdB on carboxysomes to equidistantly space carboxysomes from one another, ensuring metabolic homeostasis and a proper inheritance of carboxysomes following cell division. This study illuminates how widespread carboxysome positioning systems are among diverse bacteria. Carboxysomes significantly contribute to global carbon fixation; therefore, understanding the spatial organization mechanism shared across the bacterial world is of great interest.
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Affiliation(s)
- Joshua S. MacCready
- Department of Molecular, Cellular, and Developmental BiologyUniversity of MichiganAnn ArborMIUSA
| | - Lisa Tran
- Department of Microbiology and ImmunologyUniversity of MichiganAnn ArborMIUSA
| | - Joseph L. Basalla
- Department of Molecular, Cellular, and Developmental BiologyUniversity of MichiganAnn ArborMIUSA
| | - Pusparanee Hakim
- Department of Molecular, Cellular, and Developmental BiologyUniversity of MichiganAnn ArborMIUSA
| | - Anthony G. Vecchiarelli
- Department of Molecular, Cellular, and Developmental BiologyUniversity of MichiganAnn ArborMIUSA
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7
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MacCready JS, Hakim P, Young EJ, Hu L, Liu J, Osteryoung KW, Vecchiarelli AG, Ducat DC. Protein gradients on the nucleoid position the carbon-fixing organelles of cyanobacteria. eLife 2018; 7:39723. [PMID: 30520729 PMCID: PMC6328274 DOI: 10.7554/elife.39723] [Citation(s) in RCA: 56] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Accepted: 11/19/2018] [Indexed: 12/25/2022] Open
Abstract
Carboxysomes are protein-based bacterial organelles encapsulating key enzymes of the Calvin-Benson-Bassham cycle. Previous work has implicated a ParA-like protein (hereafter McdA) as important for spatially organizing carboxysomes along the longitudinal axis of the model cyanobacterium Synechococcus elongatus PCC 7942. Yet, how self-organization of McdA emerges and contributes to carboxysome positioning is unknown. Here, we identify a small protein, termed McdB that localizes to carboxysomes and drives emergent oscillatory patterning of McdA on the nucleoid. Our results demonstrate that McdB directly stimulates McdA ATPase activity and its release from DNA, driving carboxysome-dependent depletion of McdA locally on the nucleoid and promoting directed motion of carboxysomes towards increased concentrations of McdA. We propose that McdA and McdB are a previously unknown class of self-organizing proteins that utilize a Brownian-ratchet mechanism to position carboxysomes in cyanobacteria, rather than a cytoskeletal system. These results have broader implications for understanding spatial organization of protein mega-complexes and organelles in bacteria. Cyanobacteria are tiny organisms that can harness the energy of the sun to power their cells. Many of the tools required for this complex photosynthetic process are packaged into small compartments inside the cell, the carboxysomes. In Synechococcus elongatus, a cyanobacterium that is shaped like a rod, the carboxysomes are positioned at regular intervals along the length of the cell. This ensures that, when the bacterium splits itself in half to reproduce, both daughter cells have the same number of carboxysomes. Researchers know that, in S. elongatus, a protein called McdA can oscillate from one end of the cell to the other. This protein is responsible for the carboxysomes being in the right place, and some scientists believe that it helps to create an internal skeleton that anchors and drags the compartments into position. Here, MacCready et al. propose another mechanism and, by combining various approaches, identify a new partner for McdA. This protein, called McdB, is present on the carboxysomes. McdB also binds to McdA, which itself attaches to the nucleoid – the region in the cell that contains the DNA. McdB forces McdA to release itself from DNA, causing the protein to reposition itself along the nucleoid. Because McdB attaches to McdA, the carboxysomes then follow suit, constantly seeking the highest concentrations of McdA bound to nearby DNA. Instead of relying on a cellular skeleton, these two proteins can organize themselves on their own using the nucleoid as a scaffold; in turn, they distribute carboxysomes evenly along the length of a cell. Plants also obtain their energy from the sun via photosynthesis, but they do not carry carboxysomes. Scientists have tried to introduce these compartments inside plant cells, hoping that it could generate crops with higher yields. Knowing how carboxysomes are organized so they can be passed down from one generation to the next could be important for these experiments.
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Affiliation(s)
- Joshua S MacCready
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, United States
| | - Pusparanee Hakim
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Michigan, United States
| | - Eric J Young
- Department of Biochemistry, Michigan State University, East Lansing, United States
| | - Longhua Hu
- Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, United States
| | - Jian Liu
- Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, United States
| | | | - Anthony G Vecchiarelli
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Michigan, United States
| | - Daniel C Ducat
- Department of Biochemistry, Michigan State University, East Lansing, United States.,MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, United States
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8
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Hakim P, Weiss J, Degun R, Chalmers M, Kjeldgaard-Pedersen J, Sleeper M. Impact Of International And Therapeutic Referencing On Prices And Launch Optimization. Value Health 2014; 17:A563. [PMID: 27201864 DOI: 10.1016/j.jval.2014.08.1865] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Affiliation(s)
- P Hakim
- Navigant Consulting, Inc, London, UK
| | - J Weiss
- Navigant Consulting, Inc, London, UK
| | - R Degun
- Navigant Consulting, Inc, London, UK
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9
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Abstract
Aim In contrast to extensive reports on the roles of Nav1.5 α-subunits, there have been few studies associating the β-subunits with cardiac arrhythmogenesis. We investigated the sino-atrial and conduction properties in the hearts of Scn3b−/− mice. Methods The following properties were compared in the hearts of wild-type (WT) and Scn3b−/− mice: (1) mRNA expression levels of Scn3b, Scn1b and Scn5a in atrial tissue. (2) Expression of the β3 protein in isolated cardiac myocytes. (3) Electrocardiographic recordings in intact anaesthetized preparations. (4) Bipolar electrogram recordings from the atria of spontaneously beating and electrically stimulated Langendorff-perfused hearts. Results Scn3b mRNA was expressed in the atria of WT but not Scn3b−/− hearts. This was in contrast to similar expression levels of Scn1b and Scn5a mRNA. Immunofluorescence experiments confirmed that the β3 protein was expressed in WT and absent in Scn3b−/− cardiac myocytes. Lead I electrocardiograms from Scn3b−/− mice showed slower heart rates, longer P wave durations and prolonged PR intervals than WT hearts. Spontaneously beating Langendorff-perfused Scn3b−/− hearts demonstrated both abnormal atrial electrophysiological properties and evidence of partial or complete dissociation of atrial and ventricular activity. Atrial burst pacing protocols induced atrial tachycardia and fibrillation in all Scn3b−/− but hardly any WT hearts. Scn3b−/− hearts also demonstrated significantly longer sinus node recovery times than WT hearts. Conclusion These findings demonstrate, for the first time, that a deficiency in Scn3b results in significant atrial electrophysiological and intracardiac conduction abnormalities, complementing the changes in ventricular electrophysiology reported on an earlier occasion.
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Affiliation(s)
- P Hakim
- Physiological Laboratory, University of Cambridge, Cambridge, UK
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10
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Biswas TK, Sengupta P, Green R, Hakim P, Biswas B, Sen S. Properties of mitochondrial DNA polymerase in mitochondrial DNA synthesis in yeast. Acta Biochim Pol 1995. [DOI: 10.18388/abp.1995_4590] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Mitochondrial DNA polymerase from Saccharomyces cerevisiae, purified 3500 fold, was separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis into three polypeptides. The major 150 kDa polypeptide was probably the catalytic subunit of the mitochondrial (mt) DNA polymerase and the other two polypeptides could be either proteolytic cleavage products of the polymerase, other subunits of the enzyme or protein contaminants. The mtDNA polymerase preferred an A+T-rich DNA template and did not require any RNA primer for DNA synthesis, at least under in vitro reaction conditions. It showed higher processivity on a double-stranded linear DNA template than on a single-stranded circular DNA template, and was capable of synthesizing at least about 1200 nucleotide primer-extended products without any major pause on a double-stranded DNA template.
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11
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Abstract
This study is an historical analysis of food consumption and nutrition in Chile emphasizing the influence of political and economic factors on nutritional standards. It attempts to document and explain the persistence of malnutrition as a widespread social problem in Chile even as the country achieved a relatively advanced state of economic development and boasted an unusually progressive record of social legislation. The major findings of the study were: (a) Chile's pattern of development, social reform efforts notwithstanding, consistently discriminated against low-income groups, and (b) this discrimination perpetuated low standards of nutrition and low levels of food consumption among the country's poor and undermined the effectiveness of specific measures to alleviate malnutrition.
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